1. Field of the Invention:
The present invention relates to a system for processing color TV signals with amplitude modulation encoded chrominance information.
2. Description of the Related Art:
Color TV signals (e.g. PAL (European format) or NTSC (U.S.A. format)) are generally unsuitable for encoding through unidimensional or bidimensional high efficiency transform.
Although it is possible to apply a unidimensional or bidimensional transform to a PAL or NTSC TV signal, two problems arise in doing so:
(1) Spreading of energy over a high number of coefficients occurs when transforming base band signals.
(2) Limitations on the dimensions of the transform or, alternatively, lack of connection between the image geometry and the block on which the transform operates.
A color TV signal is a composite signal which can be expressed by the following formula: EQU s(t)=y(t)+c1(t).times.COS (2PI.times.Fscxt)+c2(t).times.SIN (2PI.times.Fscxt) (1)
where:
y(t) is the luminence signal; PA1 C1(t), c2(t) are the chrominance signals; PA1 PI is a constant; PA1 Fh is the line frequency; and PA1 Fsc is the chrominance subcarrier frequency which equals (1135/4+1/625).times.Fh for PAL and 455/2.times.Fh for NTSC)
In the presence of uniform images signals, y, c1, c2 are constant; however, the composite signal s(t) is not constant because modulation introduces an alternating current component.
Consequently, when an encoding transform is applied to the composite signal, a large number of non-zero coefficients will arise even if the image remains still, and the compression efficiency is significantly decreased as compared to the case in which the transformed signals are base band signals y(t), c1(t), c2(t).
The problem may be solved by inserting a demodulator between the signal source and the encoder. By doing so, compression efficiency improves, but the signal quality considerably degrades, and costs increase considerably because the demodulation circuitry is quite expensive.